Recently, there have been made studies and developments of systems that use an airship kept flying in the stratosphere in the altitude range of 15 to 25 kilometers, in which weather conditions are relatively stable, for the purpose of communication, broadcast, and earth observation. (See patent documents 1 and 2).
Although aircrafts capable of flying in the stratosphere have been developed, technologies that allow humans to stay in the stratosphere for a long period of time have not been known.